ISIS supporters (file)
ISIS supporters (file)Reuters

The global recruitment pull of the brutal Islamic State (ISIS) terrorist group continues to surprise, as three American teenage girls from a suburb of Denver were stopped in Germany on their way to join ISIS in Syria, US officials revealed Tuesday.

The three girls are all US citizens, and consist of two sisters of Somali origins aged 15 and 17, and a 16-year-old friend from a Sudanese family, according to sources in Denver cited by CNN.

A local Sheriff's office report quoted in the Denver Post detailed how the two sisters told their father by phone that they were feeling sick and going to the library on Friday morning.

When their friend's father came over later in the day and said his daughter had gone missing with her passport, the father of the sisters found his daughters' passports missing too - along with $2,000 - and alerted authorities.

The FBI reacted quickly to flag the passports, leading the three to be stopped in the Frankfurt airport on Friday, and flown back to Denver on Sunday. FBI spokesperson Sue Payne in Denver said "the juveniles are safe and reunited with their families."

Apparently the ISIS trio were planning to join the jihadists in Syria via Turkey, where they planned to fly to from Germany. The FBI is currently reviewing their computers to see how they were recruited and who helped arrange the flights for the teens.

According to Malak Eldie, a member of Denver's Sudanese community, the Sudanese friend who joined the two sisters was recruited after "they got her to go by saying 'if you do this it will good for Islam.' She didn't go to fight America."

ISIS has already explained that Islam calls for non-Muslim women to be forced into sexual slavery, and likewise recently stoned a woman accused of adultery.

This is in fact not the first time Denver teens have been arrested trying to join ISIS.

This July, Shannon Maureen Conley (19) was arrested at Denver International Airport as she was on her way to join the group in Syria. She pleaded guilty of providing material support to terrorists, and faces a potential five-year sentence and $250,000 fine when sentenced in January.

ISIS has been engaged in intensive recruiting targeting a western audience, and the attraction of Islamic jihad recently led 100 French girls and women to leave to join the group and serve as wives, concubines or babysitters as revealed earlier this month.

Most shockingly, several of those joining from France were shown to be Jewish girls who converted to Islam, including one who tried to blow up her parents' store.